making a mag field

Something like this from Pasco?

George H.

The relay is 11 mm along its longest axis, and I guess we should rotate it all sorts of ways to find its most sensitive position in the field.

That's cool. The gap is plenty big, but I can't tell if we could get the field down to 600 gauss. Given that example, the idea of putting magnets on the face of a vise looks practical.

We'd need a gaussmeter, not a bad thing to have anyhow.

(I can't imagine why our customer would expect a VME module to ever see a 600 gauss field.)

Thanks

ACK! All the searches for "gaussmeter" turn up ELF sensors and ghost detectors!

--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation

Try gaussmeter or gauss meter instead:

To measure the field you could just move the board and measure the generated voltage. ;-)

But then I'd need a board velocity meter!

We'd probably put the relay on a hacked test board so we could get it into the field at various orientations. We'd pulse the coil and look at the contacts and verify that it's still a relay.

Semi-serious DC Hall gaussmeters with probes seem to be around $350 each, except FW Bell, who is 3x that. Ghost detectors start around $50.

Den onsdag den 18. december 2013 22.05.42 UTC+1 skrev John Larkin:

aren't the ghost meters much lower fields? how about?

or if you really want cheap:

not terribly accurate but I guess you could calibrate at some lower field

-Lasse

That's cool. I could check its cal with a simple loop coil.

Yeah, but that would be a bunch of work.

Den onsdag den 18. december 2013 22.44.14 UTC+1 skrev John Larkin:

afaict from a quick look it is just the gain that can be from 1mV/G to 1.75mV/G

the same simple loop coil and few currents should do

-Lasse

How about MuMetal foil? ...Jim Thompson

Double-faced tape and an iPhone?

We've got a three-axis one kicking around. I think it's pretty drifty at uT levels.

That last one's not bad. Of course if it's only 600 gauss you can just put a steel can around it.

Cheers

Phil Hobbs

First option is to wind a Helmholtz coil to get a fairly homogenous volume in space with good access. Lots of info online, my quick calculation says with a diameter of 20 cm, spaced 10 cm apart, you need 6600 ampere-turns to get 60 gauss. Wind 1000 turns on each coil and put 6.6 amps through them in series, and from memory the homogeneity will be in the percent or better range for a sphere about 1 cm dia. I think the book "Building Scientific Instruments" has a good discussion, too - every analytical chemist should have that book on the shelf and regularly reread it :-).

Second option, go to

Get one of those 3-1/2 digit 3 tesla max meters off ebay to measure and map and you are in business. Adjust the tube length as needed to change the field. Go wild and thread two pieces together so you can just unscrew them a little to drop the field :-). If you really want a better estimate of the uniformity over some volume download the free program femm and model it, or send me an email and I'll run it for you.

We have a requirement to design a gadget that will work in a 0.06T static magnetic field, and we want to use some miniature telecom type relays. They are not specified for field tolerance. So we need to make such a field and test them.

A simple ring coil of 2 cm radius needs 2000 ampere-turns, kind of messy.

I guess we could buy a big lab-type electromagnet, but that's a hassle.

Maybe something could be done with a couple of these, back-to-back in a steel pipe.

If course, we'd have to get some sort of field sensor to calibrate it. With a ring coil, or a solenoid, we could just do the math.

If we had a sensor, maybe we could hack up something with PMs and bits of iron or something. Maybe pave the faces of a machinists's vise with supermagnets?

Any ideas?

Anybody got a big lab magnet?

I ordered the $180 ebay field meter that Lasse suggested. I think I'll try putting lots of little round supermagnets on the faces of a machinist's vise, which should have a pretty good magnetic circuit. George's Pasco link suggests that that might work.

I'll post pics.

Yes, option 2 sounds better to me, too, but I wanted to point out that the coils aren't that bad to make and since you sell magnet drivers I kind of figured that part would be trivial for you :-). I think lots of little magnets are going to have terrible uniformity, which is why I suggested the two larger discs. When you order the little ones, get a pair of big ones, too, just to try them. It's only $3, after all.

I ordered the $180 ebay field meter that Lasse suggested. I think I'll try putting lots of little round supermagnets on the faces of a machinist's vise, which should have a pretty good magnetic circuit. George's Pasco link suggests that that might work.

I'll post pics.

Mumetal will effectively disappear at field strengths like that.

Best regards, Spehro Pefhany

Getting haunted in your search?

Hall effect based industrial strength Gauss meters are routinely available. Years ago at LBNL, I remember using one to measure the magnetic field along the axis of cylindrical mu-metal magnetic shields. These mu-metal shields were used to protect photomultiplier tubes used in nuclear physics experiments.

We had a permanent magnet and an electromagnetic that produed about 0.5T hrough a gap of 1 inch with a face about 4 by 4 inches at least.

The thing weighed 1800 pounds and the electromagnetic had water cooled wiring taking something like 3 kW

Do you have access to any friends working in ion implantation? Somewhere in Silicon Valley should be a source. The magnetic fields those thing generate with a control of better than 0.1% would do your task easily.